Numerical simulation of unsteady state heat transfer in horizontal continuous casting with cyclic withdrawal

Abstract

Solidification during horizontal continuous casting of low carbon steel billets with cyclic withdrawal was simulated and the wavy profile of the solidifying shell characteristic of this process was reproduced. Effects of rate of withdrawal cycle, superheat and casting speed were determined. In order to carry out this simulation in a personal computer, efficient numerical techniques had to be developed for mesh refinement by coordinate transformation, interfaces with temperature discontinuities and re-entrant corners. A flexible means of mesh generation involving polynomials was also developed. From the transient heat transfer model finite difference equations peculiar to each gridpoint in the solution field were derived and solved by the Alternating Direction Implicit (ADI) method. Graphics software were developed to view the results with 3-D as well as contour plots. The heat transfer model was verified with published results of vertical continuous casting of Mg alloys and steel. Due to its ability to deal with interfaces, unlike previous work, the present model could solve temperature at both casting and mold simultaneously. A model for the shell growth, rupture and healing at the break-ring of horizontal continuous casting molds was incorporated into the heat transfer model. An interesting result of this simulation was the presence of transient hot spots in the hot face of the mold. Elimination of such hot spots should aid shell strength and hence the casting rate. A semi-quantitative dependence of the depth of the primary witness mark on cycle rate was also established.